1. Field of the Invention
The present invention relates to a device for controlling head units provided in a magneto-optical recording-reproduction device by which information is recorded on a magneto-optical disc, information recorded on the magneto-optical disc being reproduced, or being erased from the magneto-optical disc.
2. Description of the Related Art
In a magneto-optical disc used in a magneto-optical recording-reproduction device, a 5.25 inch double sided type magneto-optical disc is known in which information can be recorded on two surfaces of the disc, the information recorded on the two surfaces can be erased, and can be reproduced, according to ISO (International Organization for Standardization) standards. The erasing, recording and reproducing operations on the magneto-optical disc are carried out by a magneto-optical recording-reproduction device having a fixed magnetic head generating a bias magnetic field, and an optical head.
In this kind of magneto-optical disc, a known method of recording, reproduction and erasing of information on a magneto-optical disc can be carried out by magnetic field modulation. According to a recording operation by the magnetic field modulation method, new information can be easily overwritten on a track on which old information has been stored. The magneto-optical recording-reproduction device, which can overwrite information on the magneto-optical disc, has an optical head for radiating a laser beam onto the magneto-optical disc to record information on the magneto-optical disc and reproduce the information, and a fixed magnetic head imposing a modulated magnetic field on the magneto-optical disc to overwrite information on the magneto-optical disc.
When reproducing information stored on the magneto-optical disc, the magneto-optical recording-reproduction device radiates a laser beam onto the magneto-optical disc from the optical head, and receives the beam reflected from the magneto-optical disc by a photo detector. When overwriting information on the magneto-optical disc, the magneto-optical recording-reproduction device imparts a modulated magnetic field for recording the information, onto a point of the magneto-optical disc onto which the laser beam is also radiated from the optical head.
In the magneto-optical recording-reproduction device using the magnetic field modulation method, there is a device in which a floating magnetic head is provided as the magnetic head. By using this floating magnetic head, information can be recorded on the magneto-optical disc with high density.
The magneto-optical disc used in the magneto-optical recording-reproduction device having the floating magnetic head is a single sided type magneto-optical disc on which information can be overwritten only on one surface of the disc, which is different from the double side type magneto-optical disc for which the fixed magnetic head is used. This is due to a construction in which the floating magnetic head needs to be brought close to the magneto-optical disc.
Accordingly, even when the double-sided type magneto-optical disc is mounted in the magneto-optical recording-reproduction device in which the floating magnetic head is provided, information cannot be recorded on the double sided type magneto-optical disc.